没食子酸对锡电解精炼过程的影响

Influence of gallic acid on tin electrorefining process

传统锡电解精炼采用H2SO4 SnSO4甲酚磺酸电解液体系,然而,甲酚磺酸气味重、有毒有害,亟待寻找新型绿色环保添加剂替代甲酚磺酸。通过线性扫描、Tafel测试、滴定分析和扫描电子显微镜对比研究了甲酚磺酸和没食子酸对电解液稳定性和Sn(Ⅱ)阴极沉积行为的影响。结果表明:没食子酸的还原性强于甲酚磺酸的还原性,显著抑制析氢副反应。添加没食子酸可以使电解液酸度维持稳定,而且Sn(Ⅱ)浓度和Sn(Ⅱ)占总锡(S(T))比例保持在较高水平。相较于甲酚磺酸,没食子酸更有利于提高电解液稳定性。甲酚磺酸显著阻滞Sn(Ⅱ)的沉积,增强阴极极化,阴极锡致密平整,甲酚磺酸平整效果好。然而,没食子酸对Sn(Ⅱ)沉积动力学影响小,其阴极锡平整度、致密度低于甲酚磺酸体系的,添加高浓度没食子酸甚至会导致锡枝晶产生。木质素磺酸钠作为一种整平剂,与没食子酸复合添加可以显著改善阴极锡的平整度和致密度,两者组成的复合添加剂有望取代甲酚磺酸成为新型锡电解精炼电解液绿色添加剂。

Traditional tin electrorefining proceeds in electrolyte containing H2SO4,SnSO4 and cresol sulfonic acid(CSA).It is urgent to search novel environmental electrolyte additive to replace CSA due to its stench and toxicity.Influences of CSA and gallic acid(GA)on electrolyte stability and Sn(Ⅱ)electrodeposit behavior were comparatively investigated through linear scanning voltammetry,Tafel test,titration analysis and SEM.The results show that GA presents stronger reducibility than that CSA does,and remarkably inhibits hydrogen evolution side reaction.Addition of GA stabilizes electrolyte acidity,and enhances Sn(Ⅱ)concentration and Sn(Ⅱ)/Sn(T)ratio.Compared with CSA,GA is more suitable to enhance electrolyte stability.Addition of CSA apparently inhibits Sn(Ⅱ)electrodeposition and increases cathodic polarization.Therefore,CSA presents excellent flattening effect.However,GA shows smaller influence on Sn(Ⅱ)electrodeposition dynamic,and decreases the flatness and compactness of cathodic tin.Moreover,addition of GA in high concentration results in the appearance of tin dendrites.Sodium ligninsulfonate(SL),as a leveling agent,is selected and combined with GA.Composite additive of SL and GA is demonstrated to improve compactness and flatness of cathodic tin.Consequently,SL-GA composite additive is a potential alternative to CAS.It could be a novel environmental-friendly additive for tin electrorefining.